Lumped constant delay line



Feb. 27, 1968 M. NAIMAN LUMPED CONSTANT DELAY LINE Filed Feb. 21. 1963 INVENTOR MARK NA/MAN A T TORNE Y United States Patent Ofilice 3,371,294 LUMPED CONSTANT DELAY LINE Mark Naiman, South Lincoln, Mass, assignor to Sperry -Rand Corporation, New York, N.Y., a corporation of Delaware Filed Feb. 21, 1963, Ser. No. 260,195

11 Claims. (Cl. 333-41) This invention relates to a'signal delay line, and in particular to a'delay line of the lump parameter type.

A shortcoming of prior art lumped constant delay lines has been that they are generally expensive and difiicult to fabricate. This has been apparent whenever it has been necessary to employ numerous delay line sections consisting of individual inductors with an associated capacitor. However, improved signal rise time is obtained relative to a fixed delay time by increasing the number of sections. Therefore, by increasing the number of sections in order to obtain improved signal rise time, there results an increase in expense and difiiculty of manu- I facture.

It is therefore an object of this invention to provide an improved lumped constant delay line.

It is therefore an object of this invention to provide a lumped constant delay line which is relatively simple to fabricate.

It is a further object of this invention to provide a lumped constant delay line which is relatively economical -to fabricate.

It is a further object of this invention to provide a lumped constant delay line which may provide an improved ratio of signal delay to signal rise time at reduced cost.

It is a further object of this invention to provide a lumped constant delay line which is relatively simple to adjust in order to obtain more exact delay times.

It is a further object of this invention to furnish a lumped constant delay line which is adjustable so as to provide a wide range of delay times, characteristic impedance, and signal rise times.

In accordance with a feature of this invention there is provided a lumped parameter delay line Which incorporates a coaxial tube having an inner and outer conductor wherein a thin insulating material covers the inside surface of the outer conductor of the tube. The space between the inner and outer conductors of the coaxial tube is filled with alternate beads, discs or sections of ferrite and metal. The metal beads are so arranged so that they make electrical contact with the inner conductor of the coaxial tube. The alternate beads of ferrite and metal are so arranged along the longitudinal axis of the delay line to provide the necessary inductance and capacitance, respectively, so that the coaxial line operates as a lumped constant delay device.

In accordance with another feature of this invention, a wide range of delay times, characteristic impedances, and signal rise times may be provided by varying the following parameters of the delay line: the number of ferrite or metal beads along the longitudinal axis, the diameter of the inner or outer conductors of the coaxial tube, the thickness of the insulating material covering the inside surface of the outside conductor element of the coaxial line, the widths of the ferrite and metal beads, and the magnetic properties of the ferrite beads.

In accordance with another feature of this invention, precision, in the way of required signal delay, may be obtained with relative ease by adding or subtracting the beads of ferrite and metal even after the initial manufacturing and testing hasbeen accomplished. Furthermore, provided that the beads of metal andferrite are properly proportional with respect to one another, precision in the 3,371,294 Patented Feb. 27, 1968 way of signal delay may be attained without changing the characteristic impedance of the line.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when considered in conjunction with the accompanying drawing, in which a schematic representation of the subject delay line utilizing alternate beads of ferrite and metal is depicted.

In carrying out the invention, there is provided a lumped constant delay line which consists of a coaxial tube having an inner and outer conductor wherein the inner surface of the outer conductor has a thin insulating coating thereon. The required values of inductance and capacitance for the lumped constant delay line are obtained by arranging, transversely along the longitudinal axis of the coaxial tube and Within the space between the inner and outer conductors thereof alternate beads of ferrite and metal.

The ferrite beads arranged along the coaxial tube have the effect of providing a certain value of ,u (permeability), thereby providing inductance per unit length. However, the larger the diameter of the ferrite beads .(and hence the greater the inductance), the less will be the value of the lumped capacitance, since the inner and outer condoctors of the coaxial tube become more Widely separated. In order therefore to provide increased capacitance, conductive beads of metal which make electrical contact with the inner conductor of the coaxial tube, are inserted alternately along with the ferrite beads. The effect thereof is to reduce the separation between the inner and outer conductors of the coaxial tube and thus the capacitance per unit length is increased.

According to this arrangement, many delay line sections consisting of inductance and capacitance (i.e., alternate beads of ferrite and metal) can be simply and economically stacked along the coaxial tube depending upon the desired delay time or rise time for a particular application. The subject embodiment also enables precision in manufacturing to be obtained for the parameters of delay time and rise time by simply adding or subtracting beads of ferrite and metal even after manufacturing and testing have been accomplished.

Referring now to the accompanying drawing, there is provided a lumped constant delay line 11 comprising a coaxial tube having an inner conductor 16 and an outer conductor 14. The delay line is provided with input terminals 9 and 13, and output terminals 15 and 17. Coated along the inside surface of the outer conductor 14 is a thin insulating material 18. The outer conductor tube 14 may be made of aluminum in which event, the insulating coating 18 can be made, for example, by anodizing and thereby coating the surface thereof with an aluminum oxide of .05 to 10 mils thickness. It should be understood that other forms of insulation may be employed, such as by flow coating or spraying with a plastic resin. The center conductor 16 may be made, for example, of solderable copper or copper plated aluminium. Within the tube and along the longitudinal axis thereof are placed alternately both metal and ferrite beads or discs. One such ferrite bead 10 and metal bead 12 are shown arranged transverse to and along the longitudinal conductor 16. As

is understood, the number of beads of ferrite and metal arranged along the coaxial tube is dependent upon the desired delay or signal rise time that is required. The metal head 12 can be made of any metal having a low resistivity; however, a preferable metal that is employed consists of solder. The solder bead 12 may be formed by pouring a predetermined amount of the fused metal into the coaxial tube 11 after a ferrite bead, such as has been placed in position. The solder in its fused state is able to provide a good electrical connection with the center conductor 16, which in the instant application, is made of copper. The fused solder, however, in the process of being formed does not wet either the ferrite bead 10 or the insulating coating 18. The ferrite bead 10 is fabricated to provide a good tight fit with the inner and outer conductors so that the molten solder will not seep past the ferrite. It is understood, of course, that a metal bead designed to have a press fit in combination with the center conductor 16 can also be provided in order to obtain a good electrical contact. Other techniques of fabricating the instant delay line consists in using a solder plated inner conductor 16 and copper beads or brass beads. Heat is applied so that an electrical connection is obtained between the conductor and metal bead by fusion of the solder.

The lumped constant delay line 11 is composed of lumped elements of inductance (L), and capacitance (C). The ferrite beads 10 and metal beads 12 arranged alternately along the longitudinal axis of the coaxial tube 11 provide the necessary inductance and capacitance, respectively, for the delay line. The delay line of the subject invention when used with electronic circuitry, has the ability to delay signals (voltages and currents) applied to the input terminals 9 and 13.

The ferrite bead 10 which has high resistivity provides the required inductance since the absence of eddy currents in the ferrite allows the permeability of the material to be effective in producing a large concentration of magnetic fiux therein. Since the inductance is directly proportional to the flux density, the ferrite beads aid in furnishing the lumped value of inductance. By employing ferrite beads of a relatively large diameter, it follows that the corresponding values of inductance are also increased. Similarly, by increasing the width of the ferrite beads, an increase in inductance can also be obtained.

By using ferrite beads of a certain diameter to provide inductance, the value of lumped capacitance of the delay line is necessarily established since the value of capacitance depends upon the separation between the inner conductor of the coaxial tube 16 from the outer conductor 14. The inner and outer conductors of the coaxial tube are equivalent to the plates of a capacitor, and hence, as the plates of a capacitor are more widely separated, the capacitance is reduced in value.

In order therefore to overcome the effect of separating the inner and outer conductors of the coaxial tube because of the ferrite beads and to provide the necessary lumped capacitance, beads of metal have been alternated with the ferrite along the longitudinal axis. As mentioned earlier the bead 12 may be made of solder which in its fused state, makes a good electrical contact with the inner conductor 16. The effect of the metal bead 12 is to bring the inner conductor 16 closer to the outer conductor 14 of the coaxial tube. This results in an increased capacitance since in effect, the plates of the capacitor have been brought closer together and hence are separated only by the dielectric or insulating material 18.

For purposes of further discussion consider that the combination of a single ferrite bead 10 and a metal bead 12 constitutes a section (N) of a lumped constant delay line. Sections can be added along the longitudinal axis of the coaxial tube in order to providea wide range of delay times or signal rise times. The added sections it required can be readily stacked along the longitudinal axis for any delay time in conformity with Equation 1.

From Equation 1 it can be seen that the total delay time (T of a lumped constant line is directly proportional to the number of sections (N) as well as the square root 4 of the inductance (L) and capacitance (C) per section. In accordance with this invention, the relative ease and economy with which the ferrite and metal beads can be fabricated thereby provides a delay line that is simple and cheap to manufacture. Increased delay times may be therefore furnished by adding more delay line sections.

By referring to Equation 2 below wherein (T is the rise time (i'.e., the time for the delayed signal to rise from 10 to 90 percent of its final value in response to a step input signal) and to Equation 1, it can be shown that by increasing the number of sections (N), there is a corresponding decrease in the rise In view of the relative simplicity and nominal additional expense of adding more sections of ferrite and metal, improved rise time can be readily achieved for a constant value of (T For many purposes, the figure of merit for a signal delay line can be expressed by the ratio T T R (i.e., the ratio of signal time delay to signal rise time). Since sections can be added at a relatively low cost, and since added sections reduce (T the figure of merit of the subject delay line may be improved at little additional expense.

In a lumped constant delay line, the nominal characteristic impedance (Z is calculated in accordance with the following equation As can be seen, the characteristic impedance of the delay line is also a function of the capacitance and inductance.

The inductance and capacitance are considered variables in Equations 1, 2 and 4 since the characteristic impedance (Z the number of sections (N), the rise time (T and the delay time (T are arbitrarily selected for a particular design application. If the above mentioned parameters are first established, individual values of L and C may be computed in accordance with Equations 1, 2 and 4. Therefore, the ferrite and metal beads may be made proportional according to diameter and Width so that they provide the required section values of L and C. Accordingly, the instant invention provides a method whereby the total delay time may be readily adjusted in the manufacturing process in order to derive a certain required value by simply adding or subtracting unit ferrite and metal beads. Therefore, the ferrite and metal beads may be combined in a predetermined proportion so that as the total delay is accurately adjusted after initial manufacture by adding or subtracting beads, the ratio of characteristic impedance (Z varies very little or remains nearly constant.

In summary, the subject invention provides a coaxial tube having an inner and outer conductor. The inner surface of the outer conductor is covered with a thin insulating material. Arranged along the longitudinal axis of the coaxial tube and transversely thereto are alternate beads of ferrite and metal. The metal bead, which is in juxtaposition to the ferrite bead is arranged so that it makes good contact with the center conductor of the coaxial tube. The beads of ferrite and metal provide the required inductance and capacitance, respectively, necessary for a delay lined the lumped constant type.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a lumped constant delay line, a coaxial transmission line means having inner and outer conductors with a space therebetween and adapted to be connected to input and output means, said outer conductor having an inner and an outer surface, insulating means covering said inner surface of said outer conductor, means comprising high resistivity sections arranged within said space provided between the inner conductor and said insulation on said outer conductor of said coaxial transmission line means, said high resistivity sections providing a lumped element of inductance, means comprising low resistivity sections arranged in juxtaposition to said high resistivity sections and connected to said inner conductor to provide a lumped element of capacitance, whereby when an input signal is applied by said input means to said coaxial transmission line, the input signal is delayed before arriving at said output means.

2. In a lumped constant delay line, a transmission line means having inner and outer conductors with a space therebetween and adapted to be connected to input and output means, said outer conductor having an inner and outer surface, insulating means covering said inner surface of said outer conductor of said transmission line means, ferrite sections arranged within said space between said inner conductor and said insulation on said outer conductor of said transmission line means to provide a lumped element of inductance, means having low resistivity disposed in juxtaposition to said ferrite sections and connected to said inner conductor to provide a lumped element of capacitance, whereby when an input signal is applied by said input means to said transmission line means, the input signal is delayed before reaching said output means.

3. In a lumped constant delay line, a transmission line means having inner and outer conductors with a space therebetween and adapted to be connected to an input and an output means, said outer conductor having an inner and an outer surface, insulating means covering said inner surface of said outer conductor of said transmission line means, means having a high resistivity arranged within said space provided between said inner and outer conductors of said transmission line means, to provide a lumped element of inductance, metal beads connected to said inner conductor to provide capacitance, said metal beads alternating in position along said transmission line with said means having a high resistivity, whereby when an input signal is applied by said input means to said transmission line means, said input signal is delayed before arriving at said output means.

4. A lumped constant delay line in accordance with claim 3 wherein said metal beads are fitted on said inner conductor of said transmission line with a press fit.

5. In a lumped constant delay line, a transmission line means having inner and outer conductors with a space therebetween adapted to be connected to an input and an output means, said outer conductor having an inner and an outer surface, insulating means covering the inside surface of said outer conductor, ferrite means arranged within said space between said inner conductor and the insulation on said outer conductor of said transmission line means and providing an inductance, metal means arranged in juxtaposition to said ferrite means and connected to said inner conductor to provide capacitance, whereby when an input signal is applied by said input means to said coaxial transmission line, said input signal is delayed before reaching said output means.

6. In a lumped constant delay line, a transmission line means having inner and outer conductors with a space therebetween and adapted to be connected to an input and an output means, said outer conductor having an inner and an outer surface, insulating means covering, the inner surface of said outer conductor, ferrite beads having a high resistivity arranged transversely to the longitudinal axis of said transmission line means and within said space, metal beads having a low resistivity arranged along the longitudinal axis of said transmission line means and within said space, said metal beads being in juxtaposition to said ferrite bead means and connected to said inner conductor, whereby when an input signal is applied by said input means to said transmission line means, said input signal is delayed before reaching said output means.

7. A lumped constant delay line in accordance with claim 6 wherein said metal beads are formed by fused solder which adheres to said inner conductor of said transmission :line.

8. A lumped constant delay line in accordance with claim 6 wherein said metal head is made of copper and said inner conductor is solder plated.

9. A lumped constant delay line in accordance with claim 6 wherein said outer conductor of said transmission line is made of aluminum.

10. A lumped constant delay line in accordance with claim 9 wherein said insulating means comprises a thin layer of aluminum oxide.

11. In a lumped constant delay line, a transmission line means having inner and outer conductors with a space there between and adapted to be connected to an input and an output means, said outer conductor having an inner and an outer surface, insulating means secured along the inner surface of said outer conductor, ferrite beads disposed within said space while being oriented along the longitudinal axis of said transmission line means and arranged transversely to said longitudinal means said ferrite means providing inductance, metal solder beads arranged within said space transversely to said longitudinal axis of said transmission line means, said holder beads being alternately stacked in juxtaposition with said ferrite beads, said solder beads being formed to make contact with said inner conductor, said solder beads providing high capacitance, whereby when an input signal is applied by said input means to said coaxial means, the input signal is delayed before arriving at said output means.

References Cited UNITED STATES PATENTS 2,619,537 11/1952 Kohn 333-31 2,688,732 9/1954 Kock 333 2,877,433 3/ 1959 Devot 33373 2,892,162 6/ 1959 Bennett 333-29 2,911,554 11/1959 Kompfner 315-35 2,911,598 11/1959 Clemenson 33329 3,099,767 7/ 1963 Gross 315-36 3,125,733 3/1964 Holinbeck 333--79 3,145,353 8/1964- Bleackley 333-242 3,191,132 6/1965 Mayer 33379 HERMAN KARL SAALBACH, Primary Examiner. O C. BARAFF, Assistant Examiner. 

1. IN A LUMPED CONSTANT DELAY LINE, A COAXIAL TRANSMISSION LINE MEANS HAVING INNER AND OUTER CONDUCTORS WITH A SPACE THEREBETWEEN AND ADAPTED TO BE CONNECTED TO INPUT AND OUTPUT MEANS, SAID OUTER CONDUCTOR HAVING AN INNER AND AN OUTER SURFACE, INSULATING MEANS COVERING SAID INNER SURFACE OF SAID OUTER CONDUCTOR, MEANS COMPRISING HIGH RESISTIVITY SECTIONS ARRANGED WITHIN SAID SPACE PROVIDED BETWEEN THE INNER CONDUCTOR AND SAID INSULATION ON SAID OUTER CONDUCTOR OF SAID COAXIAL TRANSMISSION LINE MEANS, SAID HIGH RESISTIVITY SECTIONS PROVIDING A LUMPED ELEMENT OF INDUCTANCE, MEANS COMPRISING LOW RESISTIVITY 